1. Field of the Invention
The present invention relates to a method of manufacturing a thick-film circuit component, which comprises a thick-film resistor.
2. Description of the Background Art
Examples of a thick-film circuit component comprising a thick-film resistor are a hybrid IC, an R network and the like. Such a thick-film circuit component is manufactured through steps shown in FIGS. 5 to 9 respectively.
First, a substrate 11 of an electric insulating material such as alumina is prepared as shown in FIG. 5, to support electrodes 12 made of a conductive material containing silver such as Ag or an Ag--Pd alloy. The electrodes 12 are formed by applying paste containing the conductive material onto the insulating substrate 11 by printing and thereafter firing the same.
Then, a thick-film resistor 13 of an electrically resistive material containing cermet, such as ruthenium oxide, for example, is formed on the insulating substrate 11, as shown in FIG. 6. This thick-film resistor 13 is formed by applying paste containing the electrically resistive material onto the insulating substrate 11 by printing and thereafter firing the same.
Then, a protective film 14 is formed on the insulating substrate 11, to cover the electrodes 12 and the thick-film resistor 13, as shown in FIG. 7. This protective film 14 is formed by applying glaze onto the insulating substrate 11 by printing and thereafter firing the same.
Then, the thick-film resistor 13 is trimmed as shown in FIG. 8, to attain a desired resistance value. This trimming is carried out by irradiating the thick-film resistor 13 with a laser beam which is applied from above the protective film 14, so that a groove 15 is defined in the thick-film resistor 15.
Finally, a protective coating 16 of epoxy resin, for example, is formed to cover the overall insulating substrate 11, as shown in FIG. 9. This protective coating 16 is formed by dipping the overall insulating substrate 11 in liquid resin thereby applying the resin to cover the substrate 11, and thereafter solidifying this resin. Thus, a desired thick-film circuit component 17 is obtained.
In such a thick-film circuit component 17, additional electrodes and/or a necessary wiring pattern may be formed simultaneously with the electrodes 12 shown in the figures. Further, another thick-film resistor may also be formed simultaneously with the thick-film resistor 13 shown in the figures. In addition, one or a plurality of chip electronic components may be mounted on the insulating substrate 11.
In the thick-film circuit component 17 obtained in the aforementioned manner, the protective film 14 of glaze is formed in contact with the thick-film resistor 13, to cover this thick-film resistor 13. However, the protective film 14 of glaze is not so excellent in preventing migration of the silver contained in the electrodes 12. Therefore, the silver contained in the electrodes 12 may disadvantageously migrate through the protective film 14.
Further, the groove 15 which is defined by trimming of the thick-film resistor 13 extends not only through the thick-film resistor 13 but through the protective film 14, and hence the thick-film resistor 13 is partially exposed through this groove 15. This leads to reduction in moisture resistance of the thick-film circuit component 17. Although the protective coating 16 contributes some improvement in the moisture resistance, presence of the protective coating 16 hinders cost reduction or miniaturization of the thick-film circuit component 17.